Field of the Invention
The invention relates to an electronic switch for switching a load, with a current path extending between a direct voltage terminal and a load terminal, in which a power transistor and a current sensor sensing the load current are connected, and having a control or regulating device which controls the power transistor that is dependent on the load current.
Description of the Background Art
Such an electronic switch, which is also referred to as an electronic circuit breaker or electronic relay, is used to switch a load and operates in the low voltage range (DC 24V). Such a switch is particularly suitable for use in a power distribution system, as is known, for example from EP 1 186 086 B1, which corresponds to U.S. Pat. No. 6,490,141, which is incorporated herein by reference. In this known power distribution system, a number of circuits are jointly powered by a direct current by means of, for example, a switched-mode power supply, wherein the electronic switches used also take on the functionality of an electronic circuit breaker in order to control an overload current and a short circuit in a single circuit, and in case of overload or short circuit, reliably, possibly following an active current limitation, to trigger said breaker.
In conjunction with a linear power supply, such an electronic switch is known from DE 20 302 275 A1. In a current path extending between a service terminal and a load terminal, said switch includes a power transistor (MOSFET) and a regulating device, to which for current-limiting control of the power switch (semiconductor switch), a measured value detected by a current sensor in the current path is supplied. The regulating device, which according to an embodiment includes an operational amplifier operating as a comparator, is connected to its voltage supply with a charge pump to obtain the necessary increase in voltage at its control input for the operation of the power transistor, which in turn allows for the use of a comparatively inexpensive N-channel variant of a field effect transistor (MOSFET) as the load switching element.
In practical operation of such an electronic switch with a charge pump, it has been found not only to have an undesirably high circuit topological effort, but also that the power losses of particularly 450 mW to 500 mV when connecting the known electronic switch to a 24V DC voltage network are undesirably high.